Dual frequency feed horn



Aug. 13, 1963 M. GILLER ETAL 3,100,894

DUAL FREQUENCY FEED HORN Filed March 9, 1960 IN V EN TORS MORRIS GILLERJOHN GORDON NEUBERTH fatzqwgwmw United States Patent 3,100,894 DUALFREQUENCY FEED HORN Morris Giller, Baltimore County, and John G.Neuberth, Timonium, Md., assignors to The Bendix Corporation,

a corporation of Delaware Filed Mar. 9, 1960, Ser. No. 13,783 5 Claims.(Cl. 343-756) This invention relates generally to feed horns of the typegenerally employed for radiating or receiving electromagnetic energy incooperation with a reflectlng surface for the purpose of forming ashaped beam. More particularly the present invention relates to a feedhorn which is arranged to radiate two different frequencies with crosspolarization to obtain the desired illumination of a reflector surfacefor each frequency.

In many applications it is desirable to radiate independent signals ondifferent UHF or microwave frequencies using the same antenna structurefor each fre quency. With ultra high frequencies or microwaves it isgenerally desirable to provide an antenna system which has a highlydirectional beam pattern which is adapted to obtain the maximumadvantage according to the particular service for which the antenna isintended. Where the antenna is in the form of a feed horn and a curvedreflecting surface it has heretofore been difficult to obtain thedesired illumination distribution over the curved refleeting surface atmore than one frequency for any particular feed horn used to illuminatethe surface.

It is accordingly the primary object of the present invention to providea feed horn capable of radiating widely different frequencies ofelectromagnetic energy with any desired energy distribution at eachfrequency.

A further object of the invention is to provide a feed horn capable ofradiating frequencies which differ by a factor of two to one and obtainsubstantially uniform illumination of a reflecting surface for bothfrequencies.

A further object of the invention is to provide a dual frequency hornfeed in which the sources supplying energy to the feed horn areeffectively isolated from each other.

These and other objects of .the invention will be apparent from thefollowing detail description taken in conjunction with the accompanyingdrawing in which the single FIGURE is an isometric view of a feed hornin accordance with the invention with sections partly broken away forshowing the structure.

In accordance with the present invention two different frequencies areradiated by the same hor-n structure by feeding the horn to produce TEmode energy with cross polarization to the input of the feed horn. Thedimensions of the horn are chosen with respect to the lowest frequencyradiated and modified for the higher frequency by the inclusion of oneor more pairs of parallel conductive plates arranged relative to thepolarization of the two energies radiated by the horn so as to alter theeffective dimensions of the horn for the higher frequency while havingsubstantially no effect on the horn dimensions for the lower frequency.

Referring now to the FIGURE a horn constructed in accordance with thepresent invention is shown to com prise a rectangular wave guide portion11 connected to a tapered horn section 12 the junction therebetweenbeing at the throat 13 of the horn 12. The end of the horn 12 form-s theradiating aperture 14 which may be covered with fiberglass or otherradome material 15.

The rectangular wave guide 11 may be supplied in any conventional mannerwith TE energy at the lower frequency to be transmitted polarized asindicated by the arrow 16. This energy mode at the lower frequency isexcited in the disclosed embodiment by a conductive probe 17 connectedto the inner conductor of a coaxial ice line 18. The wave guide 11 isterminated by conductive plate 19 with the result that TE energyintroduced by the probe 17 is polarized with the electric vector in thedirection of the arrow 16 and propagated down the wave guide 11 throughthe horn 12 to be radiated from the aperture 14 with any desired powerdistribution as required by a particular design. A pair of matching rods21 may be provided in the horn 12 for the purpose of matching the hornin accordance with conventional practice.

In order to radiate a substantially higher frequency through thestructure formed by the waveguide 11 and horn 12 it is necessarysubstantially to reduce the trans verse dimensions of the structure inorder to obtain the desired power distribution of the radiated energyand to suppress the propagation and radiation of higher order modes. Inorder to minimize the interaction between the two frequencies to behandled by the dual frequency horn structure of the present invention,the second frequency is introduced by means of a conductive probe 22which is connected to the center conductor of a coaxial feed line 23,the axis of the coaxial line 23 being perpendicular to the planecontaining the axis of the coaxial line 18. The probe 22 thereforeintroduces TE mode energy into the wave guide 11 with the electricvector polarized in the direction of the arrow 24. In order effectivelyto reduce the internal dimensions of the waveguide 11 with respect tothe higher frequency energy introduced by the probe 22 one or moreopposed pairs of parallel spaced conductive plates 25 are conductivelyattached to the inner walls of the waveguide 11 as shown. The plates 25have substantially no effect on energy with the electric vectorpolarized in the direction of the arrow 16 but are spaced suflicientlyclose to appear as a waveguide below cutoff to energy polarized with theelectric vector in the direction of the arrow 24. Accordingly thedimensions of the effective wave guide into which the probe 24 canpropagate energy is substantially determined by the spacing between theopposed inner edges of the plates 25.

The plates 25 taper as at 26 to be flush with the inner surface of thewaveguide 11 at the throat 13 of the horn '12. The opposed tapered edges26 effectively form a tapered horn section for the high frequency energyradiated by the probe 22.

In order to reduce the radiating aperture for the high frequency energypropagated by the probe 22, the aperture 14 is effectively reduced by aplurality of spaced parallel plates 27 connected to the inner surface ofthe horn 12. The plates 27 are wedge shaped with an angle equal to theflare angle of the horn 12 such that in the assembled position shown theopposed edges of the plates 27 are parallel. The spacing betweenadjacent plates 27 may be substantially the same as that of plates 25 toact as waveguide below cutoff for the high frequency energy. Theeffective dimension to the high frequency energy from probe 22 is,therefore, the dimension between the opposed edges of the plates 27.

In order to suppress undesirable modes propagated from the probe 22 amode suppressing structure may be employed. One form of structure whichis effective to suppress the TM mode and at the same time provideadditional matching between the horn 12 and aperture 14 comprises atransverse structure 28 made of conductive material. The mode suppressor28 may be described as being in the form of a blunt arrow having a shaft29 centrally positioned along the axis of the horn 12 and supportingmembers 31 connected at an obtuse angle and conductively connected tothe inner walls of the horn 12 at opposed points on the opposite walls.The taper between the members 31 provides additional matching betweenthe aperture 14 and the horn 12 at both of the operating frequencies andin addition serves as the structural support for the mode suppressingrod '29;

In order to terminate the high frequency waveguide structure composedofplates 25 and provide improved isolation between the feeds 22 and 17,the plates 25 are connected by conductive bars 32 which serve thepurpose of closing the high frequency waveguide formed between theplates 25. The presence of the conductive bars 32 has no appreciableeffect on the energy radiated from the probe '17 through the waveguide11.

For matching purposes it may be found desirable effectively to bow thewaveguide structure for the high frequency energy by making the centralpair of the plates 25 narrower than the remaining plates-25. .Thisstructure, as shown, has the effect of providing a wider spacing betweenthe opposed inner edges of the central pair of plates 25 giving ineffect a bowed cross section to the effective waveguide formfor the highfrequency energy.

waveguide, a rectangular horn'coupled to said waveguide and "having" 'atleast 'two' opposite side" walls diverging,

a set of spaced parallel conductive plates projecting inwardly from eachdivergent wall of said horn,'said plates being wedge-shaped andpositioned in planes parallel to the axis of propagation of said hornwith the-wide end of said wedges adjacent the aperture of said horn,:a

second set of spaced parallel conductive plates projecting inwardly fromthe walls of said waveguide and positioned in planes parallel with theplanes of .said plates-I in said horn, .the plates of said second setbeing tapered to diverge at the end adjacent the junction of saidwaveguide and said horn with the angle of taper being ap:

proximately equal to the angle of divergence of said horn,

This bowed effect is continued by the taperfof the central pair ofblades up to the point where the taper merges with the inner surfacewith the guide .11 at the throat 13.

As a specific example of an embodiment of thevinvention an antenna for Lband operation. constructed to operate over a frequency range from 570m.c.to 630 m.c.

was used to illuminate a sixty foot reflector. A two degree beam widthin the direction ofpolarizationand a transverse beam width of 5.6wasattained. -At the same time the higher frequency structurewasenergized with frequencies between 990 me. and; 113.0 m.c.. and thecorresponding beam widths were 1 .5 and 55. .Thus the antenna structuregave substantially the same coverage at two frequency bandswhich,werevseparated approximately by a factor of two-to-oneand theisolation between the two probes 17 and 22. was sufficient to havenegligible effect upon the apparatus connected to the lines 18 and 23respectively. I

While the embodiment of the antenna has been described particularly withreferenceto transmission it will the dimensions of the waveguide or hornfor the higher frequency without departing .from the spirit of theinvention. Accordingly the invention is to be limited only by the scopeof appended claims.

We claim:

1. A dual frequency antenna comprising a rectangular 3 means forcoupling electromagnetic energy of a first frequency to said waveguidein the TE mode with the electric vector normal to said plates, and meansfor coupling electromagnetic energy of a second frequency higher thansaid first frequency to said waveguide in the TE mode orthogonal to saidmode of said first frequency.

2. Apparatus according to claim 1 with additionally mode suppressionmeans; said means comprising an elongated conductive element positionedon and'aligned with. the axis of propagation of said horn.

3. Apparatus according to claim 1 in which said plates in saidwaveguideextend from the region of the junction of said how and said waveguide toan intermediate point in said waveguide, said means for coupling energyof a second frequency being located between said junction and 'saidintermediate point and said means for coupling energy of a firstfrequency being located beyond said intermediate point. 7 I .4.Apparatus according to claim 3 in which the ends of said plates in saidwaveguide at said intermediate point are connected by rods in the planeof opposed pairs of said plates and extending across the spaceseparating said pairs. I

p 5. Apparatus according to claim 4 in which said plates include acentrally located opposed pair, the spacing between the opposed edges ofsaid central pair being greater than the spacing between the opposededges of adjacent pairs.

References Cited'in the file of this patent UNITED STATES PATENTS KatzinApr. 9, 1946 2,825,060 Ruze Feb. 25; 1958 2,943,324 Sichak June 28, 1960OTHER REFERENCES

1. A DUAL FREQUENCY ANTENNA COMPRISING A RECTANGULAR WAVEGUIDE, ARECTANGULAR HORN COUPLED TO SAID WAVEGUIDE AND HAVING AT LEAST TWOOPPOSITE SIDE WALLS DIVERGING, A SET OF SPACED PARALLEL CONDUCTIVEPLATES PROJECTING INWARDLY FROM EACH DIVERGENT WALL OF SAID HORN, SAIDPLATES BEING WEDGE-SHAPED AND POSITIONED IN PLANES PARALLEL TO THE AXISOF PROPAGATION OF SAID HORN WITH THE WIDE END OF SAID WEDGES ADJACENTTHE APERTURE OF SAID HORN, A SECOND SET OF SPACED PARALLEL CONDUCTIVEPLATES PROJECTING INWARDLY FROM THE WALLS OF SAID WAVEGUIDE ANDPOSITIONED IN PLANES PARALLEL WITH THE PLANES OF SAID PLATES